Fume evacuation system for an etching machine



United States Patent 1 3,538,838

[72] Inventor Charles Ray Hillhouse 1,254,725 1/1918 Pennock 98/1 15Aurora, Missouri 2,415,471 2/1947 Dorfan 98/1 15 [211 App]. No. 783,8542,544,769 3/1951 Sperry 98/115 [22] Filed Dec. 16, 1968 3,106,92710/1963 Madwed 98/115 [45] Patented Nov1ol97o rimar Exami erWilliam J.We [73] Assignee TasopeLlmited 5 & Powell y Aurora, Missouri acorporation of Missouri [54] FUME EVACUATION SYSTEM FOR AN ETCHINGMACHINE Claims 7 Drawing Figs ABSTRACT: The fume evacuation systemncludes a tank for an etchant bath, the tank housing rotating paddlesWhlCll [52] [LS-Cl 98/33, agitate the etcham bath, throwing it intoContact with the 98/115 workpiece causing a fume blanket to form abovethe etchant [51] Int. Cl F34f 13/00 l L The tank includes from and rearhollow sidewalls [50] Field ofSearch 98/33,ll5, vided with air inletvents admitting fresh from the HSLH- mosphere, and an exhaust outletvent serviced by an exhaust fan. Fresh air is drawn from the inlet ventsover the etchant [56] References cued bath, replacing the exhaustedfumes. Switching means actuate UNITED STATES PATENTS the paddles and theexhaust damper in sequence, so that the 1,085,742 2/1914 Leffel 98/115lid may then be safely opened after etching.

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Patented Nov. 10, 1970 Patented 3Nov. 10, 1970 Sheet Q of 2 Q Q )4:nae/Mi sy FUME EVACUATION SYSTEM FOR AN ETCI'IING MACHINE BACKGROUND OFTHE INVENTION This invention relates generally to fume evacuationsystems for etching machines, and in particular, to an evacuation systemfor exhausting the fumes resulting from the chemical reaction between anacid etchant and the workpiece-coating agent.

The use of acid in etching processes results in the creation of fumesand, particularly in a closed etching machine, these fumes accumulateunless a ventilation system is provided suitable for their evacuation.Before the advent of the socalled powderless etching process in theearly l950s, it was customary to disperse the cumulative fumes bycontinuous ventilation systems and a variety of such systems weredevised.

Powderless etching which speeds up the etching process, presented aparticular problem in this respect, because an excessive amount ofventilation tended to cause the etching bath to evaporate. Rather thanrisk the loss of the etchant from evaporation, etching machines usingthe powderless process were, in general, fitted with a simple vent pipeusually leading to a central venting system in which a fan was ofteninstalled.

The problem as it related to the powderless etching process becameaggravated with the recent development of new additives to form theprotective filming agent. These additives speed up the etching processbut require the use of much larger quantities of etching acid than wasthe case with heretofore usual powderless etching baths. Thus, muchgreater quantities of objectionable fumes were created, and yet the sameobjection to continuous ventilation, the evaporation of the etchantbath, remained.

The problem of evaporation is further aggravated in those etchingsystems in which the etchant bath is agitated in one way or anotherduring the etching process.

SUMMARY OF THE INVENTION This fume evacuation system works at fulleffectiveness for a short duration substantially in sequence with theetching cycle. The short duration of the fume evacuation cycle resultsin a minimum loss of the etchant by evaporation. The structuralarrangement of the air inlet venting and the fume outlet venting furtherassists in reducing evaporation of the etchant to a minimum.

The fume evacuation system includes a closeable tank for an etchantbath, the tank having agitating means therewithin, operatively agitatingthe etchant bath and throwing it into contact with the workpiece,whereby a fume blanket is created above the nominal etchant level. Airinlet vent means disposed above the etchant bath level communicates withthe tank. An exhaust means evacuates the fumes, the exhaust meansincluding-outlet vent means also disposed above the etchant bath level.Switching means operatively interconnect the agitating means and theexhaust means, and actuate the agitating means and the exhaust means inthat sequence to evacuate the fume blanket.

The tank includes opposed, sidewalls. The inlet vent includes aperturemeans located in one of the sidewalls, and the outlet vent meansincludes aperture means located in the other of the sidewalls. Eachhollow sidewall includes an inner wall and an outer wall. The inlet ventmeans includes an aperture disposed in the outer wall and an offsetaperture disposed in the inner wall, the hollow sidewall providing apassage intercommunicating between ofiset apertures.

The air inlet vent means includes an air scoop means disposed on theouter face of the outer wall which directs air into the outer wallaperture. The inner wall includes a cover spaced inwardly therefrom anddisposed in overlapping relation with the air inlet aperture in theinner wall to provide a peripheral air gap transverse to the axis of theair inlet aperture The outlet vent means includes an outlet vent pipe,and the peripheral gap has an annular area at least as great as the areaof outlet vent pipe.

The exhaust means includes an exhaust fan, and a damper plate disposedin the outer vent pipe, the plate beingactuated to an effective openposition substantially at the end of the etching cycle.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of theetching machine with the lid in an open position;

FIG. 2 is a plan view of the etchant bath tank of the etching machine;

FIG. 3 is a front elevational view of the etchant bath tank;

FIG. 4 is aside elevational view of the etchant bath tank;

FIG. 5 is an enlarged fragmentary cross-sectional view taken on line 5-5of FIG. 2 through the rear sidewall, (a view on line 5'5' taken throughthe front sidewall would be similar);

FIG. 6 is an enlarged fragmentary view in cross section taken on line6-6 of FIG. 2 through the front sidewall, (a view on line 6'-6' takenthrough the rear sidewall would be similar); and

FIG. 7 is a line diagram showing a representation of the electricalswitching.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now by characters ofreference and first to FIG. I, it will be understood that the etchingmachine generally indicated by numeral 10 includes an operationalcabinet 11 i a hydraulic ram 17 and has a structural arrangement whichrotates and lowersthe lid 15 so that the etching workpiece 20, disposedon the underside thereof, is downwardly facing in the closed positionand upright in the open position, the open position being shown inFIG. 1. t

The etching machine 10 includes a false front 21, having a hinged accesspanel 22. The false front 21 is shown in phantom outline in FIGS. 2 and5, but omitted for clarity in FIGS. 3 and 4.

As stated above, cabinet 11 consists essentially of the etchant bathtank 12, disposed above the refrigerating unit 18. FIGS. 2, 3 and 4 arerespectively plan, front, and side elevational views of the etchant tank12 extracted, as it were, from the operational cabinet 11, and lid 15and the linkage as sembly 16 are omitted for clarity.

The etchant tank 12 includes a hollow, front sidewall 23 having innerand outer walls 24 and 25 respectively, and a hollow, rear sidewall 26having inner and outer walls 27 and 28 as shown in FIGS. 5 and 6. Singlethickness lateral sidewalls 30 and 31 extend between the front and rearsidewalls 23 and 26. The etchant tank 12 also includes a bottom wall 35which is downwardly sloped toward a drain 36 located at the center ofthe bottom wall 35.

The lateral sidewalls 30 and 31 and the outer walls 25 and 28 of thefront and rear walls 23 and 26 respectively, include an upper, U-shapedportion which provides a peripheral seating ledge 32 for the peripheralrim 19 of the lid 15.

The front and rear outer walls 25 and 28 respectively are outwardlyturned at the lower ends to provide elongate seating lips 33 and 34 asshown in FIGS. 4 and 5.

The etchant tank 12 houses a paddle assembly which includes a pluralityof shaft-mounted paddle units 40 and 41, each of which is journaled atits ends into the front and rear sidewalls 23 and 26. Access to thejournaling in the front sidewall 23 is by access panel 22.

The paddle units 40 and 41 have axes of rotation somewhat above thelevel of the etchant bath 42. When rotated, the paddle units 40 and 41constitute an agitating means throwing etchant upwardly onto theworkpiece 20. It is the reaction of the acid etchant 42 on theprotective filming agent with which the workpiece is coated, that isprincipally responsible for the objectionable fumes developed within theclosed etchant tank 12.

The venting of the tank to disperse these fumes is located in the frontand rear sidewalls 23 and 26. Except for the number of aperturesemployed, the structural arrangement of the air inlet vent means in boththe front and rear sidewalls 23 and 26 is essentially the same, and forthis reason, the same reference numerals have been utilized to indicatecorresponding parts except that, on the drawings, those parts located onthe rear sidewall 26 include a prime mark.

The air inlet vent means in the front sidewalls includes a plurality ofapertures 43. An air scoop 44 is welded or otherwise attached to theouter wall 25 and serves to direct air from the atmosphere into thehollow front sidewall 23. it will be observed that the rear air scoop44' is directly accessible to the atmosphere, but that air enters thefront air scoop 44 through the side screens of the refrigeration unit 18and up behind the false front 21. In the drawings, air flow is indicatedby arrows. The air admitted into the hollow sidewall 23 passes throughsaid sidewall 23 to apertures 45. These apertures 45 are disposed in theinner wall 24 and communicate with the interior of the tank 12.

The apertures 45 include a peripheral lip 46 cupped out from the innerwall 24. The peripheral lip 46 includes a plurality of threaded socketportions 37 welded or otherwise attached thereto, to provide for thespaced connection of a cover 48 by means of a plurality of bolts 38. Thecover 48 is substantially concentric with the aperture 45 and overlapsthe aperture 45 whereby to shield the aperture 45 and prevent ingress ofetchant into the interior of the hollow sidewall 23, and to provide anannular gap 49 communicating directly with the interior of the tank 12.As is clear from H6. 6, the cover 48 also overlaps the lip 46longitudinally, further to facilitate the shielding function. Theminimum cross-sectional area of the air inlet vent means along the airflow route is preferably at least equal to the minimum exhaust area. Inparticular, the peripheral gap 49 is preferably oversize.

it will be understood that the shielding of the apertures 45 and thestaggering of the apertures 45 with apertures 43 in the outer sidewall23 tends to inhibit the outward passage of fumes to the atmosphereduring the etching cycle. The exhaust means evacuating the fumesincludes a vent pipe 50 having a transition portion i welded orotherwise attached around an outlet vent aperture 52. The aperture 52extends through the hollow sidewall 26 and is sealed off from theinterior of the hollow sidewall 26 by means of opposed side plates 53and a bottom plate 54 as is clearly indicated in FIG. 5. A butterflyvalve 56, constituting a damper means, is located in the interior of thevent pipe 50. An exhaust fan F is connected to the vent pipe 50.

The minimum exhaust vent area of the vent pipe 50 is preferably notgreater than the combined area of the inlet apertures 45 and 45 toensure rapid extraction of the fumes and replacement of clean air withinthe interior of the tank 12.

The switching arrangement, diagramatically illustrated in FIG. 7,provides that the fan F is operating continuously during the operationof the etching machine 10. The paddle motor P and a damper solenoid Dare controlled by a switch S. The switch S provides sequential actuatingof the damper solenoid D after the paddle agitation has ceased. in otherwords, the evacuation cycle substantially follows the etching cycle.

It is thought that the functional advantage of this fume evacuationsystem have become fully apparent from the foregoing description ofparts, but for completeness of disclosure, the operation of the fumeevacuation system will be briefly described.

During the etching cycle, the acid etchant thrown against the workpiecereacts with the coating thereon and causes a fume blanket to form abovethe level of the etchant bath 42. During this period, the damperprovided by the butterfly valve 56 in the vent pipe 50 is almost closed.Preferably it is open to only about 10 percent of its fully openposition. The exhaust fan is running continuously during this time,withdrawing, however, only a small amount of the fumes. The continuousrunning of the fan provides a slight exhaust pressure on the fumeblanket inhibiting the outward leakage of fumes through the air inletmeans. The continuous running of the exhaust fan F has an additionaladvantage in that it prevents a backup of fumes into the tank 12 afterthe completion of the principal exhaust cycle and before the machine isturned off. Thus when the closure lid 15 is open, there is no risk ofatmospheric pollution from fume backup.

When the etching process is substantially completed and the paddles 41have ceased their agitating rotation, a solenoid switch indicated by theletter S in FIG. 7 switches open the damper 56 to a fully open position.The exhaust fan F sucks the fume blanket through the vent pipe 51 and,at the same time, sucks in replacement fresh air through the air intakescoops 44 and 44' located on the outer walls 25 and 28 of the front andrear sidewalls 23 and 26 respectively because of the partial vacuumcaused in the tank 12.

The fresh air drawn into the air scoops 44 and 44' enters the hollowfront and rear sidewalls 23 and 26 through the apertures 43 and exitsfrom the hollow sidewalls through the offset apertures 45 and theannular gap 49 into the interior of the tank 12. The air inlet apertures45 are located at three of the four corners of the tank l2, and theoutlet aperture 52 is located at the fourth corner. Air is thus drawnacross the surface of the etching bath en route to the outlet vent pipe5b which facilitates rapid fume exhaust.

The covers 48 overlapping the apertures 45 tend to act as baffles, andthe passage between the offset apertures 44 and 45 in the front and rearsidewalls 23 and 26 tends to impede any undesirable leakage of fumes tothe atmosphere.

It will be understood that the butterfly valve 56 is switched to thefully open position automatically for a specific time period forexample, 10 or 15 seconds after the etching cycle as may be set by theoperator. The substantial damping of the exhaust means to about 10percent of full potential during the etching process preventsevaporation of the etching bath at this time. Of course, the exhaust fanF need not run continuously. And as an alternative, the exhaust fan Fand the damper means could be actuated and deactuated simultaneously, insequence with the paddle agitation means, all within the scope of theclaims hereunto appended.

I claim:

1. A fume evacuation system for a powderless etching machine comprising:

a. a tank for an etchant bath, the tank including sidewall meansextending above the etchant level;

b. agitating means in the tank operatively agitating the etchant bathand causing a fume blanket above the etchant bath level; closure meanssubstantially operatively covering the tank during agitation;

d. air inlet vent means disposed above the etchant bath level andcommunicating with the interior of the tank;

. exhaust means evacuating the fumes including outlet vent meansdisposed above the etchant bath level and communicating with theinterior of the tank; and switching means operatively interconnectingthe agitating means and the exhaust means and actuating the agitatingmeans and the exhaust means in that sequence to substantially evacuatethe fume blanket before the opening of the closure.

2. An evacuating system as defined in claim 1, in which:

g. the inlet vent means includes at least one aperture located in thetank sidewall means.

3. An evacuation system as defined in claim 1, in which:

g. the tank sidewall means includes a pair of hollow sidewalls having aninner wall and an outer wall;

h. the inlet vent means includes aperture means located in one of saidsidewalls; and

i. the outlet vent means includes aperture means located in the other ofsaid sidewalls.

4. An evacuation system as defined in claim 1, in which:

g. the tank sidewall means includes a hollow sidewall having an innerwall and an outer wall;

h. the inlet vent means includes an aperture disposed in the outer walland an aperture disposed in the inner wall, said apertures being offset;and

i. a portion of said hollow sidewall provides a passage interconnectingsaid offset apertures.

5. An evacuation system as defined in claim 4, in which:

j. the inlet vent means includes an air scoop means disposed on theouter face of the outer wall and directing air into the outer wallaperture; and

k. the inlet vent means includes a cover spaced inwardly from the innerwall and disposed in overlapping relation with the aperture in the innerwall to provide a peripheral gap transverse to the axis of the innerwall aperture.

6. An evacuation system as defined in claim 1, in which:

g. the tank sidewall means includes a pair of sidewalls;

h. at least one of the sidewalls is hollow to provide spaced inner andouter walls;

i. said one sidewall includes a pair of communicating apertures spacedin the direction of air flow to provide at least part of the inlet ventmeans;

j. the other sidewall includes an aperture providing part of the outletvent means; and

k. the outlet vent means includes an outlet vent pipe communicating withsaid other sidewall aperture.

7. An evacuation system as defined in claim 6, in which the inlet ventmeans includes an aperture area, communicating directly with the tank atleast equal to the vent pipe area.

8. An exhaust system as defined in claim 6, in which:

l. the exhaust means includes an exhaust fan and damper means disposedin the outlet vent pipe; and y m. the damper means is actuated to theopen position, substantially at the'end of the agitating cycle.

9. An evacuation system as defined in claim 1, in which:

g. the sidewall means includes front and rear hollow sidewalls eachincluding an inner wall and an outer wall;

h. the inlet vent means includes aperture means disposed in each of saidsidewalls;

i. the aperture means in each hollow sidewall includes an aperture inthe outer wall and an aperture in the inner wall, said apertures beingoffset, and a passage portion intercommunicating said offset aperturesin the direction of air flow; and

j. the inlet vent means includes an air scoop directing air into theouter wall apertures and cover means shielding each of the inner wallapertures.

10. An evacuation system as defined in claim 9; in which:

R. the outlet vent means includes an outlet aperture located in one ofthe hollow sidewalls to draw air across the etchant bath and throughthat hollow sidewall from the inlet vent means in the other of saidsidewalls;

l. the exhaust means includes an outlet vent pipe communicating with thesaid outlet aperture and an exhaust fan located within the outlet ventpipe; and

m. the exhaust means includes a damper plate controlled by the switchingmeans to be partly open during etching and fully open during exhaust.

